2020–2021 BCSC Basic and Clinical Science Course™
7 Oculofacial Plastic and Orbital Surgery
Part III: Lacrimal System
Chapter 14: Anatomy, Development, and Physiology of the Lacrimal Secretory and Drainage Systems
Physiology
Evaporation accounts for approximately 10% of tear elimination in the young and for 20% or more in elderly persons. Most of the tear flow is actively pumped from the tear lake by the actions of the orbicularis oculi muscle. Blinking pushes the tears from lateral to nasal on the eyelid margin. When the eyelids open, negative pressure pulls the tears into the sac; when the eyelids close, the action of the orbicularis muscle creates positive pressure that forces those tears through the NLD (Fig 14-4, Video 14-1). A weakened blink interferes with the normal pumping mechanism and contributes to epiphora in patients with eyelid laxity or CN VII palsy.
VIDEO 14-1 Lacrimal pump mechanism.
Courtesy of Cat N. Burkat, MD; illustration by Christine Gralapp. Access all Section 7 videos at
www.aao.org/bcscvideo_section07.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.